1. Field of the Invention
The present invention relates to an apparatus and a process for hydraulic high-pressure forming of a sheet, e.g., a blank.
2. Description of the Background Art
It has been known in the art for production of sheet metal components having a complex geometry to carry out forming with the aid of working fluids. In such a case, a working fluid pressure is applied to a sheet and the sheet is offhand formed without initially reproducing the shape of a tool on it. The sheet then gets adapted to the shape of a rigid bottom or a top tool and is brought into its desired final shape by a sizing pressure of the working fluid or by way of any conventional pressing technique (DE 196 24 036 A1). The drawbacks involved in such processes, however are very long cycle times due to the fact that the various forming steps are carried out sequentially and that pressure buildup takes place slowly. Thus, the conventional processes are not suitable for use in large-scale production of formed sheets.
Other conventional apparatus for carrying out such a process have a forming tool that includes a forming cavity defined by a bottom die and a top die. The press ram of a fixed-stroke mechanical press is connected to the top die, namely via the pressure generating unit and/or the piston/cylinder unit whose cylinder cavity is in a fluid conducting communication with the forming area of the forming tool. It is due to that arrangement that hydraulic forming may be achieved at high speed because the work piece is already being deformed under the action of the working fluid pressure from the piston/cylinder unit when the forming tool is already closed and while the press ram is still moving downward and the piston of the piston/cylinder unit is hence still descending. The hydraulic forming process is already terminated by the time the mechanical press and/or the crank of a crank press reaches its bottom dead center position.
All of these solutions, however, require comprehensive sealing provisions against the sheet so that working fluid pressure buildup may be effectively achieved. Such seals are subject to heavy wear due to a relative movement between the tool and the sheet. Thus, the need for additional sealing provisions is a major drawback especially in large-scale sheet processing.